The present invention resides generally in the field of polymers of vinylpyridines. More particularly, the present invention relates to solution polymerizations of vinylpyridine monomers to prepare linear vinyl pyridine polymers.
As further background, linear polyvinylpyridines and functionalized derivatives and copolymers thereof are useful in a wide variety of applications. For example, conductive polymers prepared from linear polyvinylpyridine and molecular iodine have been utilized as cathode materials in small solid-state batteries in which long life under low current strain is required, such as batteries used in implantable cardiac pacemakers. See, U.S. Pat. Nos. 3,660,163 (1972) and 3,773,557 (1973). Quaternary salts of polyvinylpyridines (e.g. poly(1-alkylvinylpyridinium halides)) have proven to be good negative electron beam resists for microlithography. See, K. I. Lee et al., Proc. SPIE Int. Soc. Opt. Eng., 333, 15 (1982).
Polyvinylpyridines have been used extensively in the repographic and lithographic fields because of the combination of properties ranging from adhesive to electrical properties. See, U.S. Pat. Nos. 4,041,204 (1977); 3,942,988 (1976); Ger. Offen. 3,040,047 (1981); Japan KOKAI 76 30,741 (1976); U.S. Pat. No. 4,032,339 (1977); Ger. Offen. 2,701,144 (1977); and Japan KOKAI 75 124,648 (1975). Polyvinylpyridines have also found applications in the film and photographic area. For example, solutions of polyvinylpyridine or their quaternary salts form thin films that protect the image surface of instant film prints. See, U.S. Pat. Nos. 2,874,045 (1959); 2,830,900 (1958); and 3,459,580 (1969).
Polyvinylpyridines are compatible with synthetic and natural polymers such as polyolefins (including polypropylene), polyethylene terephthalate, nylon, and cellulose, and thus find applications in plastics, alloys and blends. Fibers incorporating polyvinylpyridines show excellent dyeing intensity and are color fast [see, e.g. U.S. Pat. No. 3,361,843 (1968)] and polyvinylpyridiniumphosphate imparts permanent fire retardancy to cellulose textiles [see U.S. Pat. No. 2,992,942 (1961)] and thus polyvinylpyridines find uses in the textile industry as well.
Polyvinylpyridines further find utility in the treatment of bleached Kraft paper to increase titanium dioxide retention in pulp slurries, and electroplating applications (in particular quaternary salts), as corrosion inhibitors for metals including iron, aluminium, copper, brass, magnesium and solders, as polymerization inhibitors in Li/TiS.sub.2 current-producing electrochemical cells, as emulsion stabilizers and dispersing agents (in particular acid salt and quaternary salt forms), as flocculating agents (particularly acid salt and quaternary ethylhalide forms), in ion exchange membrane preparation and many other applications. These and other uses for linear polyvinylpyridines are reviewed extensively in product literature available from Reilly Industries, Inc., Indianapolis, Ind. U.S.A., entitled "Linear Polyvinylpyridine: Properties and Applications" (1983 and 1989), to which reference can be made for additional information.
As to their preparation, linear polyvinylpyridines have been prepared by various general polymerization techniques. These have included radiation initiated, Ziegler-Natta initiated, free radical initiated and anionic initiated polymerizations. Radiation initiated polymerizations have usually been used for the preparation of graft copolymers. Ziegler-Natta initiated systems usually do not work well for the vinylpyridine systems.
Free radical (addition) polymerizations of vinylpyridines are common in the literature. Generally, there are three differing types of free radical catalyzed polymerizations, those being solution, emulsion and bulk. They are carried out more commonly using initiators such as benzoyl peroxide, cummene hydroperoxide and azobis (isobutyronitrile). Bulk polymerization of vinylpyridine catalyzed by benzoyl peroxide, hydrogen peroxide and certain other per compounds has been reported (French Pat. 849,126 (1939); CA:35:6358.sup.6 (1941)), as has suspension polymerization of vinylpyridine catalyzed by water-soluble free radical initiator in the presence of small particles of solid polyolefin (U.S. Pat. Nos. 3,828,016, 3,947,526 and 4,824,910). Generally speaking, however, in known free radical-catalyzed processes it has often proven highly difficult to control the molecular weight of the vinylpyridine polymers using free radical initiators.
Anionic low temperature (-78.degree. C.) homopolymerization of 4-vinylpyridine initiated with certain monofunctional alkalai-metal based carbanionic species have been studied in tetrahydrofuran and other solvent mixtures as reported by S. K. Varshney et al. in Macromolecules (26) 701 (1993). A significant disadvantage of this and other anionic polymerizations (see e.g. G. E. Molan et al., J. Polym. Sci. Part A-1, 4, 2336 (1966)) is the requirement of extreme dry conditions for the polymerizations which are directly related to the M.sub.w control of the product polymer. Thus, historically, anionic polymerizations of vinylpyridines have been somewhat difficult to control, making it complicated to obtain linear polyvinylpyridines of desired molecular weights, especially at lower molecular weights.
In addition to conventional polymerization methods, vinylpyridines have been reported to spontaneously polymerize upon salt formation with acids or alkyl halides. J. C. Salamone et al., Polymer Letters, 9, 13 (1971); I. Mielke et al., Macromol. Chem. 153, 307 (1972); J. C. Salamone et al, Macromolecules, 6, 475 (1973); J. C. Salamone et al., Polymer Letters, 15, 487 (1977). Such spontaneous polymerizations are relatively disadvantageous because they give rise to a mixture of the normal linear polyvinylpyridines and ionene type polymers.
In light of this background, there are needs for improved methods for polymerizing vinylpyridine monomers so as to achieve the production of linear polyvinylpyridines of controlled molecular weight. Such improved methods would also desirably be facile to conduct using readily available and inexpensive equipment and starting materials, while providing good reaction rates and product yields. The present invention addresses these needs.